1. Field of the Invention
The present invention relates to a technique for controlling the output of a object data on the basis of accumulation time for which the object data is outputted by output means such as display and speaker.
2. Prior Art of the Invention
With improvement in digital technology and wide spread of network in recent years, contents such as image, sound, document data (hereinafter “original data”) can be instantaneously distributed to many and unspecified clients without degradation.
The client can freely see distributed original data and furthermore can copy the distributed original data on hard disk drive (HDD) and removable storage medium with little degradation.
Meanwhile, the digitized original data does not degrade in quality through many generations of copying and therefore the copy right of the original data is easy to violate as by illegal copy etc.
For example, a third party without a title can use the original data freely after the original data which is acquired via the Internet or is stored on a removable storage medium etc. was captured in personal computer etc.
To strictly protect the copy right of the original data, encrypting techniques such as CPRM (Content Protection for Recordable Media) is used in which the original data is encrypted by “encryption key” and stored on the storing medium and decoded using “decoding key.” Also, mutual authentication technique is used in which kinds of copyright protection techniques mounted on the sender and receiver of the original data are mutually confirmed and “key information” etc. are exchanged. In these methods, “private duplication” of the original data is restricted and the copyright is protected.
However, even if the coding techniques such as CPRM and mutual authentication techniques are used, a third party without a title can see the original data freely as long as the third party likes after acquiring and restoring the original data by some means. In other words, the original data can be displayed for as long as one likes after the original data is restored by the third party. Therefore, it is difficult to protect the copyright of the displayed original data.
In addition to the purpose of protecting the copyright of the original data, it is desired in some cases that the display time of the original data should be limited. For example, a content provider offers services in which, using the content provider server, questions in correspondence course of education as original data are distributed to the clients. In this service, the client sees the distributed questions, writes down answers to the questions and sends them back via the network. And the contents provider marks the returned answers and judges the client's scholastic ability.
In that case, to fairly judge the client's scholastic ability, it is necessary to limit the answering time depending on the level of the client's scholastic ability. For example, if a client with a standard scholastic ability solves 5 questions, the answering time has to be limited to one hour, and if a client with an elementary level, the answering time has to be limited to one hour and 15 minutes.
However, it is difficult to limit the answering time in the past. That is because the display time of the distributed questions can not be limited. Therefore, the client can see the acquired original data as long as the client likes and it can not be known how long it took the client to answer the question, and it is impossible to fairly judge the scholastic ability of the client.
As described, the display time of the original data can not be limited in the past.
Up to now, the task has been described on the assumption that the original data is data displayed by display means. The original data can be output by sound, and in the past the output time of the original data can not be limited. Therefore, it is difficult to protect the copyright of data after the data was restored.